The present invention relates to an illumination apparatus having an irradiation source and a liquid light guide coupled thereto. The liquid light guide comprises a flexible position retaining tube which can be directed by a human operator to an object to be illuminated and which maintains thereafter its spatial positioning.
Illumination apparatuses of this kind are known in the prior art in connection with light guides made of glass fiber bundles. They are typically used in laboratories and referred to as light sources with “goose neck” light guides. Typically, they contain an irradiation source with a tungsten/halogen-reflector lamp and one (or a plurality of) light guides made of fiber glass bundles. The light guides are positioned within a flexible armoring tube having a position retaining function. The known goose neck light guides have a total length of less than one meter which is sufficient for most applications. The outer armoring tubes which are also known as position retaining or holding tubes are commercially available and are manufactured by winding a metallic profile band with a sealing strand or wire. A special technology is responsible for the holding function after the bending.
Since light guides made of fiber glass bundles are highly flexible, the two ends of a fiber glass bundle can readily be twisted against each other. Therefore, for manufacturing a goose neck light guide, the fiber bundle can simply be inserted into the holding tube and the corresponding end portions of the fiber glass bundle at the first and second ends of the holding tube can be glued to the holding tube in order to provide a fixed connection there between. If such a goose neck light guide is then fixedly mounted at one end to the irradiation source, the other end can be freely manipulated. Due to its high inner flexibility the fiber glass bundle inside the holding tube can absorb the changes of the relative position between light guide and irradiation source caused by the manipulation, without causing strain in the fiber bundle and running the risk of damages due to broken fibers.
Liquid light guides, as described in DE 42 33 087 A1 by way of example, are known for more than 30 years in the market. Compared to light guides made of fiber glass bundles they provide the advantage of an improved transmission in the short wavelength region of the visible spectrum and in the UV region. This is particularly useful for certain laboratory applications, such as fluorescence excitation with short wavelength irradiation.
It is desired to have a goose neck arrangement for liquid light guides as well. Liquid light guides contain a fluor-carbon-tube (F-C-tube) which is filled with a liquid. This tube is also referred to as the “light guide core” and is mechanically sealed at both ends by glass plugs and sealing sleeves. In contrast to the highly flexible fiber glass bundles, liquid light guides are only semi-flexible and the two ends of the liquid light guides cannot be twisted against each other. The mechanical disadvantages of liquid light guides become more and more relevant when the diameter of the light active core gets larger, i.e. when the diameter is 3 mm or higher.
When a goose neck liquid light guide is manufactured according to the same pattern as the above described fiber glass bundles and the light input end of the light guide is fixed to a light source with a high power UV-lamp, manipulations of the light guide in use result in deformings of the F-C-tube inside the holding tube. This causes transmission losses and heats the liquid light guide locally up. After a certain amount of time during which intensive light in the region of irradiation powers of plural watts applied to the liquid light guide, there might be permanent damages and deformings of the fluor-carbon light guide tube and the optical transmission of the liquid light guide decreases drastically.